Although the use of a nitrogen atmosphere enhanced welding during welding good wetting properties , but the erection of a small element of the phenomenon often associated with low oxygen levels. However, other characteristics of the temperature curve , set the oven conveyor belt or assembly operation characteristics can cause tombstoning .
A check of the furnace , nitrogen and oxygen
In a forced air convection oven control is very important. If you do not want to accidentally brought the curtain damage from turbulence workshop environment and / or stove , it might give some small elements increase the likelihood erected . Depending on the furnace design and flow control , the flow of velocity may be too fast. But, more likely to maintain or furnace configuration issues are causing an undesirable impact on the stove direct airflow assembly .
To fully obtain the benefits of enhanced nitrogen wetting force , often the maximum 2000ppm 500ppm or a desired maximum level of oxygen. However , some devices used to reduce the concentration of oxygen in nitrogen to 100ppm - this is not a necessary process . The above problem is erected only occurs when elements with nitrogen , and only in a specific PCB. This fact shows that speed may be fast enough moist , but not enough on a particular pad - get such a conclusion , the temperature curve may need to look at. Perhaps, increasing the concentration of oxygen to prevent this problem.
In the case with and without nitrogen stream , to assemble a combination of PCB board for temperature curve , the thermal galvanic occurred in the upright position , so that may help. If the component is connected to the ground pad on the PCB , may be measured to uneven heating . In this case , the PCB to the ground a good way to increase the thermal limit of the apparatus to solve the problem , if the temperature control problem can be solved .
Second, the problem of weldability
Remember, erected and with the wetting force change rate related to wet - all the components and the PCB board and should show sufficient performance may be sustained . Solderability problems are often overlooked , the machine is set tone over tone in the past , that is the way to solve the problem of solder joint defects . Weldability particularly important element for 0201 and 0402 because of small differences in wetting properties of this component are likely to produce a big difference . Between the bonding side, the sheet-like element of any suspicious opposite end , or any large temperature difference may cause solderability erected .
